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Revaluation of Structural Properties of
Machine Stress Graded Plywoods Revised November 2012
PROJECT NUMBER: PNB194-1011 DECEMBER 2011
PROCESSING
This report can also be viewed on the FWPA website
www.fwpa.com.au FWPA Level 4, 10-16 Queen Street,
Melbourne VIC 3000, Australia
T +61 (0)3 9927 3200 F +61 (0)3 9927 3288
E info@fwpa.com.au W www.fwpa.com.au
Revaluation of Structural Properties of Machine Stress Graded Plywoods
Prepared for
Forest & Wood Products Australia
by
Doug Gaunt
Forest & Wood Products Australia Limited Level 4, 10-16 Queen St, Melbourne, Victoria, 3000 T +61 3 9927 3200 F +61 3 9927 3288 E info@fwpa.com.au W www.fwpa.com.au
Publication: Revaluation of Structural Properties of Machine Stress Graded Plywoods Project No: PNB194-1011 This work is supported by funding provided to FWPA by the Australian Government Department of Agriculture, Fisheries and Forestry (DAFF). © 2011 Forest & Wood Products Australia Limited. All rights reserved. Whilst all care has been taken to ensure the accuracy of the information contained in this publication, Forest and Wood Products Australia Limited and all persons associated with them (FWPA) as well as any other contributors make no representations or give any warranty regarding the use, suitability, validity, accuracy, completeness, currency or reliability of the information, including any opinion or advice, contained in this publication. To the maximum extent permitted by law, FWPA disclaims all warranties of any kind, whether express or implied, including but not limited to any warranty that the information is up-to-date, complete, true, legally compliant, accurate, non-misleading or suitable. To the maximum extent permitted by law, FWPA excludes all liability in contract, tort (including negligence), or otherwise for any injury, loss or damage whatsoever (whether direct, indirect, special or consequential) arising out of or in connection with use or reliance on this publication (and any information, opinions or advice therein) and whether caused by any errors, defects, omissions or misrepresentations in this publication. Individual requirements may vary from those discussed in this publication and you are advised to check with State authorities to ensure building compliance as well as make your own professional assessment of the relevant applicable laws and Standards. The work is copyright and protected under the terms of the Copyright Act 1968 (Cwth). All material may be reproduced in whole or in part, provided that it is not sold or used for commercial benefit and its source (Forest & Wood Products Australia Limited) is acknowledged and the above disclaimer is included. Reproduction or copying for other purposes, which is strictly reserved only for the owner or licensee of copyright under the Copyright Act, is prohibited without the prior written consent of FWPA. ISBN: 978-1-921763-36-6
Researcher/s: Douglas Gaunt Scion Private Bag 3020 Rotorua 3046 New Zealand Rob McGavin Department of Employment, Economic Development and Innovation 50 Evans Road Salisbury Queensland 4107
i
Executive Summary
The aim of this project was to relate the strength and stiffness properties of current
softwood/hardwood plywood resources from both Australian and New Zealand against the
existing published plywood stress grades.
The primary goals for this project were based around the following;
The plywood standard AS/NZS2269.0:2008 and the timber design standard AS1720.
1:2010 list different grade stresses for the same plywood grades and the designers of
plywood structures can choose either standard for the basis of their structural designs.
Which set of grade stresses are the most appropriate and should there be any grade
stress amendments.
The plywood standard AS/NZS2269.0:2008 lists three techniques for determination of
plywood stress grades, two of which were not in existence when the original plywood
strength properties were developed. Thus are the existing plywood grades and
strength/stiffness properties still relevant and applicable to the machine stress grading
(MSG) approach to grading of plywood for todays softwood and hardwood resource?
Key Recommendations
The Australian designers of plywood structures should use the characteristic values
from AS1720.1:2010.
The characteristic plywood stresses in AS/NZS2269.0:2008 should either by amended
to reflect those in AS1720.1:2010 or deleted leaving AS1720.1:2010 as the only source.
The planned revision of NZS3603:1993 should be aligned with the AS/NZS4063 series
in which normalisation has been discontinued. NZS3603 should also adopt the
appropriate plywood grades and characteristic stresses from AS1720.1:2010.
Consideration should be given to the introduction of lower shear values in
AS1720.1:2010 on the proviso that there are no significant impacts on the structural use
of plywood and/or the plywood shear test method in AS/NZS2269.1:2008 should be
reviewed to improve its ability to produce true shear failures
Impact
With the confirmation of the current grade stresses (apart from shear) in AS 1720.1 it is
anticipated that there will be minimal impact on the design use of plywood. Plywood
designers should have a renewed confidence in the strength properties of plywood which
could reflect in a greater use.
Confirmation that the plywood grade stresses in AS 1720.1:2010 align well with the F8, F11
& F14 plywood resource from both Australia & New Zealand should be of comfort to the
plywood producers. This implies that the producers will not have to make significant
changes to their plywood production methods.
Disclaimer
The plywood used in this study was selected using a plywood machine stress grader in an
effort to understand the effect of machine stress grading plywood on plywood properties. In
the report the F rating that has been assigned is that from the machine stress grader, it is not
the company branded F ratings. In fact the machine grader sample was made up from a mix
of non-structural, downgrade (material with sound bonding), F5, F8 & F11 (company
branded) plywood, this was done to maximise the property range within the machine grader
sample.
ii
Tables 5 and 6 primarily show the ineffectiveness of machine stress grading plywood. The
samples of plywood in Tables 5 & 6 are not representative of company branded product and
accordingly the results cannot be interpreted as such.
All the New Zealand plywood used in report was kindly provided from one mill. It is also
worth acknowledging that no machine graded softwood plywood is sold in NZ.
The companies producing plywood currently operate under a third party verification scheme
and accordingly end users can have confidence that structural plywood will have the
properties claimed for it.
Table of Contents
Executive Summary .................................................................................................................... i Introduction ................................................................................................................................ 1 Methodology .............................................................................................................................. 2
Plywood Sampling ................................................................................................................. 2 Mechanical Test Methods ...................................................................................................... 2 Plywood Section Properties ................................................................................................... 4 Results .................................................................................................................................... 5
Discussion - Grade stress ........................................................................................................... 9 Grade Stress Observations ................................................................................................... 14
Discussion - Shear Testing ....................................................................................................... 19
Discussion - Machine Stress Grading Relationships ................................................................ 21 Machine stress grading observations.................................................................................... 24
Conclusions .............................................................................................................................. 26 Recommendations .................................................................................................................... 26 References ................................................................................................................................ 27 Acknowledgements .................................................................................................................. 27 Researcher’s Disclaimer ........................................................................................................... 27 Appendix A .............................................................................................................................. 28
1
Introduction
The aim of this project was to relate the strength and stiffness properties of current
softwood/hardwood plywood resources from both Australian and New Zealand against the
existing published plywood stress grades. The current plywood grades in the timber design
and plywood standards have been in existence for many years and were originally derived
from small, clear sample testing of hardwoods originating from the forest resource of the
1960’s or earlier.
The primary goals for this project were based around the following;
The plywood standard AS/NZS2269.0:2008 and the timber design standard AS1720.
1:2010 list different grade stresses for the same plywood grades and the designers of
plywood structures can choose either standard for the basis of their structural designs.
Which set of grade stresses are the most appropriate and should there be any grade
stress amendments.
The plywood standard AS/NZS2269.0:2008 lists three techniques for determination of
plywood stress grades, two of which were not in existence when the original plywood
strength properties were developed. Thus are the existing plywood grades and
strength/stiffness properties still relevant and applicable to the machine stress grading
(MSG) approach to grading of plywood for todays softwood and hardwood resource?
This project has tested of eight batches of machine graded plywood made up of a mix of
Australian produced softwood and hardwood plywood along with New Zealand produced
softwood plywood. The plywood F-grades selected for testing are estimated to cover 80-85%
of F-grades sold in Australia and 100% of New Zealand..
2
Methodology
Plywood Sampling
The plywood for this project was selected in conjunction with advice from the EWPAA as
follows in Tables 1 & 2.
The plywood was supplied in kind by many of the plywood mills and it was not the intention
of this project to evaluate the ability of the individual plywood mills to achieve the grade
characteristic properties. Accordingly no reference will be made to the original suppliers of
the plywood other than referencing by country, species and machine stress grade. Each batch
represents one mill.
The plywood for batches 1, 2, 3, 4, 5, 6 & 8 was selected under the guidance of the EWPAA
using the mills plywood machine stress grader. Essentially over the period of one/two days
plywood of various grades was taken from stock and passed through the machine stress grader
until the required machine rated target grades/thicknesses had been selected.
Table 1: Plywood sheets received and tested by Scion
Plywood
NZ
Radiata
F11
(Batch 1)
NZ
Radiata
F8
(Batch 2)
Australian
Radiata
F8
(Batch 3)
Australian
Radiata
F11
(Batch 4)
Number of 12mm sheets 12 12
Number of 15mm sheets 21 17 12 12
Number of 17mm sheets 14 18 10 12
Total Number of sheets to be tested 35 35 34 36
Received and tested by Scion Scion Scion Scion
Table 2: Plywood sheets received and tested by DEEDI
Plywood
Australian
Slash
F11
(Batch 5)
Australian
Slash
F14
(Batch 6)
Australian
Plantation
Hardwood
(Batch 7)
Australian
Hardwood
F34
(Batch 8)
Number of 12mm sheets 18 12
Number of 15mm sheets 6 12 32/48* 35
Number of 17mm sheets 11 11
Total Number of sheets to be tested 35 35 32/48* 35
Received and tested by DEEDI DEEDI DEEDI DEEDI
* 32 compression & Tension tests, 48 bending & shear tests.
Note: The F-grade is that assigned from the machine stress-grader and is not the grade of the
input material.
Mechanical Test Methods
1. All the plywood sheets were machined graded at source with the assistance of the
EWPAA. The plywood was then supplied to the testing agency. On arrival the machine
grading information was recorded and the plywood sheets cut into the test specimens in
accordance with AS/NZS2269.1:2008.
2. The bending strength and stiffness specimens were tested to destruction in accordance
with AS/NZS2269.1:2008.
3
3. The tension strength specimens were tested to destruction in accordance with
AS/NZS2269.1:2008.
4. The compression strength specimens were tested to destruction in accordance with
AS/NZS2269.1:2008.
5. The shear strength specimens were tested to destruction in accordance with
AS/NZS2269.1:2008
6. The strength and stiffness data was analysed in accordance with AS/NZS2269.2:2008 and
AS/NZS4063.2:2010 using the parametric, log normal method.
4
Plywood Section Properties
In order to calculate the final strength and stiffness properties the plywood section properties
are needed. Tables 3 and 4 show the values used for this project.
Table 3: Plywood Bending Section Properties Used.
Parallel
to 2.4m panel length
(Parallel
Direction)
Perpendicular
to 2.4m panel length
(Perpendicular
Direction)
Batch No: Plywood
Type:
Plywood
Thickness
Source of Section
Property values
Section
Modulus
(Z)
Moment of
Inertia (I)
Section
Modulus
(Z)
Moment of
Inertia (I)
(mm3/mm) (mm
4/mm) (mm
3/mm) (mm
4/mm)
1 5 ply 15mm Manufacturer 28.7 218.2 14.3 73.8
1 5 ply 17mm Manufacturer 33.3 281.9 20.2 120.2
2 5 ply 15mm Manufacturer 28.7 218.2 14.3 73.8
2 5 ply 17mm Manufacturer 33.3 281.9 20.2 120.2
3 12-24-05 12mm AS/NZS2269.0:2008 19.0 115.0 8.3 33.0
3 15-30-05 15mm AS/NZS2269.0:2008 29.5 225.0 13.0 65.0
3 17-24-07 17mm AS/NZS2269.0:2008 33.5 285.0 19.0 120.0
4 12-24-05 12mm AS/NZS2269.0:2008 19.0 115.0 8.3 33.0
4 15-30-05 15mm AS/NZS2269.0:2008 29.5 225.0 13.0 65.0
4 17-24-07 17mm AS/NZS2269.0:2008 33.5 285.0 19.0 120.0
5 12-24-05 12mm AS/NZS2269.0:2008 19.0 115.0 8.3 33.0
5 15-30-05 15mm AS/NZS2269.0:2008 29.5 225.0 13.0 65.0
5 17-24-07 17mm AS/NZS2269.0:2008 33.5 285.0 19.0 120.0
6 12-24-05 12mm AS/NZS2269.0:2008 19.0 115.0 8.3 33.0
6 15-30-05 15mm AS/NZS2269.0:2008 29.5 225.0 13.0 65.0
6 17-24-07 17mm AS/NZS2269.0:2008 33.5 285.0 19.0 120.0
7 - 15mm DEEDI values* Plywood manufactured as part of a separate research
project, Section properties calculated for each sheet
8 15-30-05 15mm AS/NZS2269.0:2008 29.5 225.0 13.0 65.0
* Calculated using the EWPAA software “EZ Calc”
5
Table 4: Plywood Compression/Tension Section Areas Used.
Parallel
to 2.4m panel length
(Parallel
Direction)
Perpendicular
to 2.4m panel length
(Perpendicular
Direction)
Batch No: Plywood
Type:
Plywood
Thickness
Source of Section
Property values
Number of
plies
Thickness
of plies
Number of
plies
Thickness
of plies
(mm) (mm)
1 5 ply 15mm Manufacturer 3 8.46 2 6.58
1 5 ply 17mm Manufacturer 3 8.46 2 8.28
2 5 ply 15mm Manufacturer 3 8.46 2 6.58
2 5 ply 17mm Manufacturer 3 8.46 2 8.28
3 12-24-05 12mm AS/NZS2269.0:2008 3 7.20 2 4.80
3 15-30-05 15mm AS/NZS2269.0:2008 3 9.00 2 6.00
3 17-24-07 17mm AS/NZS2269.0:2008 4 9.60 3 7.20
4 12-24-05 12mm AS/NZS2269.0:2008 3 7.20 2 4.80
4 15-30-05 15mm AS/NZS2269.0:2008 3 9.00 2 6.00
4 17-24-07 17mm AS/NZS2269.0:2008 4 9.60 3 7.20
5 12-24-05 12mm AS/NZS2269.0:2008 3 7.20 2 4.80
5 15-30-05 15mm AS/NZS2269.0:2008 3 9.00 2 6.00
5 17-24-07 17mm AS/NZS2269.0:2008 4 9.60 3 7.20
6 12-24-05 12mm AS/NZS2269.0:2008 3 7.20 2 4.80
6 15-30-05 15mm AS/NZS2269.0:2008 3 9.00 2 6.00
6 17-24-07 17mm AS/NZS2269.0:2008 4 9.60 3 7.20
7 - 15mm DEEDI values* Plywood manufactured as part of a separate research
project, Section properties calculated for each sheet
8 15-30-05 15mm AS/NZS2269.0:2008 3 9.00 2 6.00
* Calculated using the EWPAA software “EZ Calc”
Results
The characteristic strength and stiffness properties have been calculated using the calculation
methods and procedures set out in AS/NZS2269.2:2008 and AS/NZS4063.2:2010
(parametric, log normal method)
Tables 5 and 6 show the characteristic strength and stiffness values by Batch number
(plywood sizes combined) with the assigned
(AS1720.1:2010 ‘F’ grade) and the
[AS/NZS2269.0:2008 ‘F’ grade] by test.
Tables 7, 8 & 9 list the characteristic plywood design stresses from AS1720.1:2010,
AS/NZS2269.0:2008 and NZS3603:1993.
Appendix A, Tables A1 & A2 list the coefficients of variation & 5th
percentile data for each
test and by batch number.
6
Table 5: Summary of AS1720.1:2010 characteristic test results for the combined sample
Batches 1, 2, 3 & 4.
Characteristic Strength Properties (MPa)
Strength Property Plywood Test
Direction
NZ
Radiata
F8
(Batch 1)
NZ
Radiata
F11
(Batch 2)
Australian
Radiata
F8 grade
(Batch 3)
Australian
Radiata
F11 grade
(Batch 4)
Bending stiffness Parallel
9665
(F8)
[F8]
10720
(F11)
[F11]
8970
(F7)
[F7]
10432
(F8)
[F8]
Bending stiffness Perpendicular
10014
(F8)
[F8]
9598
(F8)
[F8]
11440
(F11)
[F11]
10290
(F8)
[F8]
Bending strength Parallel
28.61
(F8)
[F8]
33.05
(F11)
[F8]
29.36
(F8)
[F8]
32.65
(F11)
[F8]
Bending strength Perpendicular
28.60
(F8)
[F8]
25.97
(F8)
[F8]
33.02
(F11)
[F8]
34.00
(F11)
[F8]
Tension strength Parallel
17.43
(F8)
[F8]
17.75
(F8)
[F8]
19.23
(F11)
[F8]
21.30
(F11)
[F11]
Tension strength Perpendicular
14.78
(F7)
[F7]
12.26
(F7)
[F7]
20.12
(F11)
[F11]
14.72
(F7)
[F7]
Compression
Strength Parallel
40.05
(F17)
[F17]
29.17
(F14)
[F11]
31.97
(F14)
[F14]
30.66
(F14)
[F14]
Compression
Strength Perpendicular
36.92
(F17)
[F14]
29.14
(F14)
[F11]
35.56
(F14)
[F14]
35.23
(F14)
[F14]
Shear Strength Parallel
5.30
(F11)
[F11]
5.72
(F14)
[F11]
5.48
(F11)
[F11]
5.30
(F11)
[F11]
Shear Strength Perpendicular
5.66
(F14)
[F11]
6.02
(F17-F34)
[F11]
5.74
(F14)
[F11]
5.77
(F14)
[F11]
(F11) denotes the AS1720.1:2010 grade
[F8] denotes the AS/NZS22669.0:2008 grade
7
Table 6: Summary of AS1720.1:2010 characteristic test results for the combined sample.
Batches 5, 6, 7 & 8.
Characteristic Strength Properties (MPa)
Strength Property Plywood Test
Direction
Australian
Slash
F11 grade
(Batch 5)
Australian
Slash
F14 grade
(Batch 6)
Australian
Plantation
Hardwood
(Batch 7)
Australian
Hardwood
F34
(Batch 8)
Bending stiffness Parallel
10151
(F8)
[F8]
12285
(F14)
[F14]
12934
(F14)
[F14]
22678
(F34)
[F34]
Bending stiffness Perpendicular
12109
(F14)
[F14]
12311
(F14)
[F1R4]
13736
(F14)
[F14]
21396
(F27)
[F27]
Bending strength Parallel
35.83
(F11)
[F11]
44.54
(F14)
[F14]
38.20
(F14)
[F11]
99.56
(F34)
[F27]
Bending strength Perpendicular
41.36
(F14)
[F14]
41.20
(F14)
[F14]
40.30
(F14)
[F14]
91.11
(F34)
[F27]
Tension strength Parallel
30.34
(F17)
[F17]
28.86
(F17)
[F14]
30.33
(F17)
[F17]
67.13
(F34)
[F34]
Tension strength Perpendicular
23.43
(F14)
[F11]
23.12
(F14)
[F11]
23.43
(F14)
[F11]
52.67
(F27)
[F27]
Compression Strength Parallel
27.30
(F14)
[F11]
29.73
(F14)
[F11]
34.64
(F14)
[F14]
66.85
(F27)
[F27]
Compression Strength Perpendicular
23.31
(F11)
[F8]
40.93
(F17)
[F17]
43.50
(F17)
[F17]
66.6
(F27)
[F27]
Shear Strength Parallel
5.46
(F11)
[F11]
5.05
(F11)
[F8]
5.91
(F14)
[F11]
6.52
(F17-F34)
[F14]
Shear Strength Perpendicular
5.07
(F11)
[F8]
5.12
(F11)
[F8]
6.01
(F17-F34)
[F11]
6.51
(F17-F34)
[F14]
(F11) denotes the AS1720.1:2010 grade
[F8] denotes the AS/NZS22669.0:2008 grade
Note:
The batch 7 material was produced by DEEDI using veneers from four species of plantation
logs, the plywood was laid-up to suit the objectives of another project, and as such is not
directly comparable with production plywood. The test data does however show relativity
between the strength results which fit with the other test data collected.
8
Table 7: Characteristic stresses for structural plywood (MPa)
(Moisture content 15% or less) from AS1720.1:2010
Stress
Grade
Bending Tension Panel
Shear
Compression
in the plane
of the sheet
Bearing
Normal to
the plane of
the sheet
Modulus
of
Elasticity
Modulus
of
Rigidity
f’b f’t f’s f’c f’p E G
F 34 90 54 6.0 68 31 21500 1075
F 27 70 45 6.0 55 27 18500 925
F 22 60 36 6.0 45 23 16000 800
F 17 45 27 6.0 36 20 14000 700
F 14 36 22 5.5 27 15 12000 625
F 11 31 18 5.0 22 12 10500 525
F 8 25 15 4.5 20 9.7 9100 455
F 7 20 12 4.2 15 7.7 7900 345
Table 8: Characteristic stresses for structural plywood (MPa)
(Moisture content 15% or less) from AS/NZS2269.0:2008
Stress
Grade
Bending Tension Panel
Shear
Compression
in the plane
of the sheet
Bearing
Normal to
the plane of
the sheet
Modulus
of
Elasticity
Modulus
of
Rigidity
f’b f’t f’s f’c f’p E G
F 34 100 60 6.8 75 31 21500 1075
F 27 80 50 6.8 60 27 18500 925
F 22 65 40 6.8 50 23 16000 800
F 17 50 30 6.8 40 20 14000 700
F 14 40 25 6.1 30 15 12000 625
F 11 35 20 5.3 25 12 10500 525
F 8 25 15 4.7 20 9.7 9100 455
F 7 20 12 4.2 15 7.7 7900 345
F 5* 14 9.6 3.8 12 6900 345
* EWPAA Industry Standard F5 grade
Table 9: Characteristic stresses for structural plywood (MPa)
(Moisture content 15% or less) NZS3603:1993
Compression
Stress
grade
Bending Tension Panel
Shear
Rolling
Shear
In the
plane
of the
sheet
normal
to the
plane of
the sheet
Modulus
of
elasticity
Modulus
of
rigidity
fpb fpt fps fpt fpc fpp E G
F 22 57.6 34.6 6.0 2.4 43.2 20.4 16000 800
F 17 44.5 26.7 6.0 2.4 33.4 17.3 14000 700
F 14 36.7 22.0 5.4 2.2 27.5 13.6 12000 625
F 11 28.8 17.3 4.7 1.9 21.6 10.7 10500 525
F 8 22.5 13.5 4.2 1.7 16.9 8.6 9100 455
9
Discussion - Grade stress In order to understand the relationship between the AS/NZS2269.1:2008 test stiffness and
strength properties and the published grade stresses the following figures have been produced.
Figure 1: Bending stiffness parallel versus bending stiffness perpendicular
Figure 2: Bending MoE parallel versus Bending Strength parallel
Figure 3: Bending MoE parallel versus Bending Strength perpendicular
Figure 4: Bending MoE parallel versus Compression Strength parallel
Figure 5: Bending MoE parallel versus Compression Strength perpendicular
Figure 6: Bending MoE parallel versus Tension Strength parallel
Figure 7: Bending MoE parallel versus Tension Strength perpendicular
Figure 8: Bending MoE parallel versus Shear Strength parallel
Figure 9: Bending MoE parallel versus Shear Strength perpendicular
In these figures the characteristic bending stiffness in the parallel direction is used for
comparison with the other characteristic stiffness and characteristic strength properties.
The data could be represented by using the bending stiffness in the parallel direction value for
the claimed grade against the as tested strength properties. For instance if the plywood was
sold as F11 then the bending stiffness in the parallel direction value would be the code value
of 10,500MPa (not the as tested value) and the other strength properties would those as tested.
This approach would be useful in confirming compliance with standards however for this
study the intent was to look at relationships between test properties.
Plotted in these figures are the:
1. Strength and stiffness properties for the plywood batches 1 – 8 (One set of
characteristic values per batch).
2. Strength and stiffness properties from 13 Scion client data sets. This information is
limited to comparison purposes only, no links can be made to the supplier or the
plywood as the raw data remains confidential to the original Scion client.
3. The plywood from batch's 1, 2, 3, 4, 5 & 6 as sorted by the machine stress graded
(MSG) parameter (see below).
4. Characteristic strength and stiffness values as taken from AS1720.1:2010.
5. Characteristic strength and stiffness values as taken from AS/NZS2269.0:2008.
6. Characteristic strength and stiffness values as taken from NZS3603:1993.
Plywood machine stress grade re-sort.
The combined data from Batches 1, 2, 3, 4, 5 & 6 MSG was re-sorted by computer using the
plywood machine stress grading (MSG) data in conjunction with the mechanical test data.
Essentially different MSG grade thresholds were applied and then the corresponding
characteristic stiffness and strength were calculated. These calculated values were then
compared with required code values for that grade. Further adjustments were made to the
thresholds (bearing in mind that any adjustment also affects the grades above and below) as
necessary. The aim was to just achieve the stiffness and strength properties for each grade
with a primary focus of achieving the bending parallel stiffness.
This resorting reflects the procedures MSG producers could use in practice ie. linking back
the QA bending strength and stiffness data back to machine stress graders thresholds (grade
cut off points).
The combination of the six batches was only done to provide sufficient data for the analysis to
be done, it is accepted that a plywood mill will not be using the combination of raw material
in the six batches. However Scion believes for this exercise it shows the potential
relationships between the different stiffness and strength properties.
10
Figure 1: Bending MoE parallel vs Bending MoE perpendicular
Figure 2: Bending MoE parallel vs Bending Strength parallel
11
Figure 3: Bending MoE parallel vs Bending Strength perpendicular
Figure 4: Bending MoE parallel vs Compression Strength parallel
12
Figure 5: Bending MoE parallel vs Compression Strength perpendicular
Figure 6: Bending MoE parallel vs Tension Strength parallel
13
Figure 7: Bending MoE parallel vs Tension Strength perpendicular
Figure 8: Bending MoE parallel vs Shear Strength parallel
14
Figure 9: Bending MoE parallel vs Shear Strength perpendicular
Grade Stress Observations
The characteristic grade stresses are very similar between AS1720.1:2010 and
NZS3603:1993. Whereas AS/NZS2269.1:2008 lie above both AS1720.1:2010 and
NZS3603:1993.
It should be noted that AS1720.1:2010 is now aligned with new AS/NZS4063 series in
which normalisation has been discontinued which now leaves AS/NZS4063 entirely
material related. AS/NZS2269 and NZS3603 are now corresponding not aligned with
the new AS/NZS4063 series.
In order to summarise the data shown on Figures 1 – 9 the following Tables 10 – 17 show the
number of data points (Batches) falling below the three lines of characteristic plywood
stresses ie.. AS1720.1:2010, AS/NZS2269.1:2008 & NZS3603:1993.
Bending stiffness parallel versus bending stiffness perpendicular
More of the data points lie above the characteristic stiffness (all three standards) line. This
indicates that the bending stiffness perpendicular is higher than the bending stiffness parallel.
Bending stiffness parallel versus Bending strength parallel
Table 10: Number of data points falling below the characteristic stresses.
- Bending Strength parallel
AS1720.1:2010 AS/NZS2269.1:2008 NZS3603:1993
Data from this study 1 4 1
Scion Data 1 3 1
MSG data 0 0 0
15
Bending stiffness parallel versus Bending strength perpendicular
Table 11: Number of data points falling below the characteristic stresses
- Bending Strength perpendicular
AS1720.1:2010 AS/NZS2269.1:2008 NZS3603:1993
Data from this study 2 3 1
Scion Data 2 2 2
MSG data 1 1 0
Bending stiffness parallel versus Compression strength parallel
Table 12: Number of data points falling below the characteristic stresses
- Comp Strength parallel
AS1720.1:2010 AS/NZS2269.1:2008 NZS3603:1993
Data from this study 1 1 0
Scion Data 0 1 0
MSG data 0 0 0
Bending stiffness parallel versus Compression strength parallel
Table 13: Number of data points falling below the characteristic stresses
- Compression Strength perpendicular
AS1720.1:2010 AS/NZS2269.1:2008 NZS3603:1993
Data from this study 2 1 0
Scion Data 0 0 0
MSG data 0 0 0
Bending stiffness parallel versus Tension strength parallel
Table 14: Number of data points falling below the characteristic stresses
– Tension Strength parallel
AS1720.1:2010 AS/NZS2269.1:2008 NZS3603:1993
Data from this study 0 1 0
Scion Data 0 1 0
MSG data 0 0 0
Bending stiffness parallel versus Tension strength perpendicular
Table 15: Number of data points falling below the characteristic stresses
– Tension Strength perpendicular
AS1720.1:2010 AS/NZS2269.1:2008 NZS3603:1993
Data from this study 4 5 3
Scion Data 2 3 2
MSG data 1 2 1
Bending stiffness parallel versus Shear strength parallel
Table 16: Number of data points falling below the characteristic stresses
Shear Strength parallel
AS1720.1:2010 AS/NZS2269.1:2008 NZS3603:1993
Data from this study 1 3 1
Scion Data 2 3 2
MSG data 0 1 0
16
Bending stiffness parallel versus Shear strength perpendicular
Table 17: Number of data points falling below the characteristic stresses
– Shear Strength perpendicular
AS1720.1:2010 AS/NZS2269.1:2008 NZS3603:1993
Data from this study 1 3 1
Scion Data 1 2 1
MSG data 0 1 0
From Figures 1 - 9 and Tables 10 - 17:
1. The characteristic plywood grade stresses in AS1720.1:2010 appears to provide at
better fit then those in AS/NZS2269 with the data. A significant factor is the fact that
AS1720.1:2010 is now aligned with new AS/NZS4063 series in which normalisation
has been discontinued.
2. Tension strength perpendicular tends to have more data points falling below
characteristic plywood grade stresses. This could be associated with a tendency in
production to use lower visual grade veneers in the cross bands which then can have a
negative impact on tension strength; this also impacts on bending perpendicular
strength. In Scions opinion after witnessing a large number of tests this impact does
not appear in compression perpendicular or shear perpendicular testing.
3. Potentially the shear grade values for AS1720 could be amended downwards slightly
however questions do exist about the shear test itself (see Shear test section in report).
Figures 10 & 11 shows a potential revision with Tables 18 & 19 listing the potential
shear stresses.
Figure 10: Bending MoE parallel vs Shear Strength parallel revision
17
Figure 11: Bending MoE parallel vs Shear Strength perpendicular revision
Table 18: Characteristic stresses for structural plywood (MPa)- Revision
(Moisture content 15% or less) from AS1720.1:2010
Stress
Grade
Bending Tension Current
Panel
Shear
Proposed
Panel
Shear
Compression
in the plane
of the sheet
Bearing
Normal to
the plane of
the sheet
Modulus
of
Elasticity
Modulus
of
Rigidity
f’b f’t f’s f’c f’p E G
F 34 90 54 6.0 6.0 68 31 21500 1075
F 27 70 45 6.0 6.0 55 27 18500 925
F 22 60 36 6.0 5.5 45 23 16000 800
F 17 45 27 6.0 5.1 36 20 14000 700
F 14 36 22 5.5 4.8 27 15 12000 625
F 11 31 18 5.0 4.5 22 12 10500 525
F 8 25 15 4.5 4.3 20 9.7 9100 455
F 7 20 12 4.2 4.0 15 7.7 7900 345
(Revised shear stresses shown highlighted)
18
Table 19: Characteristic stresses for structural plywood (MPa) -Revision
(Moisture content 15% or less) NZS3603:1993
Compression
Stress
grade
Bending Tension Current
Panel
Shear
Proposed
Panel
Shear
Rolling
Shear
In the
plane
of the
sheet
normal
to the
plane of
the sheet
Modulus
of
elasticity
Modulus
of
rigidity
fpb fpt fps fps fpt fpc fpp E G
F 22 57.6 34.6 6.0 5.5 2.4 43.2 20.4 16000 800
F 17 44.5 26.7 6.0 5.1 2.4 33.4 17.3 14000 700
F 14 36.7 22.0 5.4 4.8 2.2 27.5 13.6 12000 625
F 11 28.8 17.3 4.7 4.5 1.9 21.6 10.7 10500 525
F 8 22.5 13.5 4.2 4.3 1.7 16.9 8.6 9100 455
(Revised shear stresses shown highlighted)
Prior to any revision of grade stresses the use of the new stresses should be tested in the
market via a design study to review the impact on the use of plywood in structures. For
instance will the reduced stresses now make some plywood designs less economic?
19
Discussion - Shear Testing
The plywood shear method in AS/NZS2269.1:2008 requires 200x85 plywood specimens to
which steel rails are bolted each side and then tested, as Figure 12
Figure 12: Plywood Shear test configuration
On undertaking this shear testing Scion consistently observes that the maximum test load is
not always associated with a shear failure but often related to a bolt bearing failure (Figure
13). In Figure 13 the specimen on the left has generated a shear failure whereas the specimen
on the right has produced a bolt bearing failure. The concern is that if the method was
improved to always generate a shear failure then the calculated shear stresses could also be
improved. It is suggested that this issue be directed to the relevant AS/NZS plywood
standards committee.
This data should further be interrogated to examine the numbers of bolt bearing failures with
their failure loads versus true shear failures this would further develop and refine this issue.
However this work was outside the original scope of this project.
A topic for further discussion from this study is:
Should the AS1720 characteristic shear stresses be amended to suit the test data
or should the test method be amended to improve the failure shear stresses?
21
Discussion - Machine Stress Grading Relationships The plywood machine stress grader grades whole sheets of plywood by measuring bending
stiffness along in the parallel direction (parallel to the 2.4m sheet length.) by applying load
and measuring the resultant deflection. Figure 14 shows a plywood machine stress grader.
.
Figure 14: Plywood machine stress grader.
In order to investigate the ability of plywood machine stress grading the data has been pooled
to cover the plywood grades F8, F11 and F14, this range reflects that which could be expected
to be produced from a radiata pine or slash pine plywood operation.
The following Figures 15 – 24 show the relationship between the whole sheet bending parallel
MoE (the plywood machine stress grader value) and the ten AS/NZS2269 plywood strength
and stiffness properties, Table 20 lists the regression coefficients.
Table 20: R2 regression coefficients
Measured Property Predicted AS/NZS2269 Property Regression Coefficients R2
Whole Sheet MoE Bending MoE parallel 0.4199
Whole Sheet MoE Bending MoE perpendicular 0.0699
Whole Sheet MoE Bending strength parallel 0.1808
Whole Sheet MoE Bending strength perpendicular 0.0820
Whole Sheet MoE Compression strength parallel 0.1798
Whole Sheet MoE Compression strength perpendicular 0.0520
Whole Sheet MoE Tension strength parallel 0.2985
Whole Sheet MoE Tension strength perpendicular 0.1822
Whole Sheet MoE Shear strength parallel 0.0235
Whole Sheet MoE Shear strength perpendicular 0.1193
22
Figure 15: Sheet MoE vs MoE parallel Figure 16: Sheet MoE vs MoE perpendicular
Figure 17: Sheet MoE vs Bending parallel Figure 18: Sheet MoE vs Bending perpendicular
y = 0.7269x + 2518.6R² = 0.4199
0
2000
4000
6000
8000
10000
12000
14000
16000
5000 7000 9000 11000 13000 15000
Mo
E P
ara
llel
Sheet MoE
y = 0.539x + 5776.6R² = 0.0699
0
5000
10000
15000
20000
25000
5000 7000 9000 11000 13000 15000
Mo
E P
erp
Sheet MoE
y = 0.0041x + 9.4263R² = 0.1808
0
10
20
30
40
50
60
70
80
90
5000 7000 9000 11000 13000 15000
Ben
d P
ara
llel
Sheet MoE
y = 0.0039x + 18.221R² = 0.082
0
20
40
60
80
100
120
140
5000 7000 9000 11000 13000 15000
Ben
d P
erp
Sheet MoE
23
Figure 19: Sheet MoE vs Comp parallel Figure 20: Sheet MoE vs Comp perpendicular
Figure 21: Sheet MoE vs Tension parallel Figure 22: Sheet MoE vs Tension perpendicular
y = 0.0017x + 24.773R² = 0.1798
0
10
20
30
40
50
60
70
5000 7000 9000 11000 13000 15000
Co
mp
Pa
rall
el
Sheet MoE
y = 0.0011x + 36.323R² = 0.052
0
10
20
30
40
50
60
70
5000 7000 9000 11000 13000 15000
Com
p P
erp
Sheet MoE
y = 0.004x - 8.8591R² = 0.2985
0
10
20
30
40
50
60
70
80
90
5000 7000 9000 11000 13000 15000
Ten
sion
Para
llel
Sheet MoE
y = 0.0049x - 13.411R² = 0.1822
0
10
20
30
40
50
60
70
80
90
5000 7000 9000 11000 13000 15000
Ten
sio
n P
erp
Sheet MoE
24
Figure 23: Sheet MoE vs Shear parallel Figure 24: Sheet MoE vs Shear perpendicular
Machine stress grading observations
The only significant relationship that exists is between the sheet MoE and bending MoE in the
parallel direction only. This could reasonably be expected as both measurements are
addressing the same property. The relationships to other nine properties are very weak if
apparent at all.
This can be explained as follows:
For bending stiffness the stiffness properties of the long band veneers and the cross
band veneers are usually not linked in anyway. It is not uncommon for the cross band
veneers to be of a lower visual grade and /or lower stiffness grade..
A measurement of bending stiffness can have a strong relationship with strength when
the wood samples are small, clear and straight grained. However strength is
commonly governed by grain angle and direction, this occurs primarily around knots.
Figure 25 shows the relationship between plywood bending stiffness and plywood
bending strength in the parallel direction as taken from the same AS/NZS2269 test
specimens. This is the theoretical best case relationship and generates an R2 of only
0.4323. Taking this theoretical best relationship it becomes possible to explain the
poor relationship between sheet MoE and the other eight strength properties.
Looking at the MSG data points in Figure 1-9 (three data points only) appears to show the
MSG grading better achieving all characteristic strength properties. The author believes this
apparent trend just reflects the fact that higher stiffness grade plywood has higher strength
properties as seen in the plywood characteristic design values (AS1720.1:2010)
y = 0.0001x + 5.8187R² = 0.0235
0
2
4
6
8
10
12
5000 7000 9000 11000 13000 15000
Sh
ear
Pa
rallel
Sheet MoE
y = 0.0003x + 4.4799R² = 0.1193
0
2
4
6
8
10
12
5000 7000 9000 11000 13000 15000
Sh
ear
Per
pSheet MoE
26
Conclusions
The plywood characteristic grade stresses in AS1720.1:2010 provide a better fit with
the data from this study & Scion test data then those in AS/NZS2269.0:2008. The
primary factor in this, is that AS1720.1:2010 is now aligned with new AS/NZS4063
series in which normalisation has been discontinued whilst AS2269.0:2008 is out of
step with the new AS/NZS4063 series.
Ultimately the plywood stresses in the New Zealand timber structures standard
NZS3603 should be aligned with those in AS1720.1:2010.
Potential exists to amend the characteristic shear grade values in AS1720.1:2010 as
the both the data from this study & Scion test data indicate some difficulty in
achieving the required grade stresses. However concern exists whether the shear test
method in AS/NZS2269 can reliably and consistently produce a true shear failure.
With the current shear test method on observation of other Scion shear testing a true
shear does not always occur with the specimens failing on occasions in bolt bearing
first.
When plywood sheets are machine stress graded along the parallel direction the only
significant AS/NZS2269 mechanical test relationship in with the bending stiffness in
the parallel direction. The relationships to the other nine AS/NZS2269 mechanical
test properties are very low if apparent at all in some cases. The properties in the
parallel direction are not always linked to the properties in the perpendicular direction
as in Scion observations there is a tendency on occasions in production to use lower
visual grade veneers in the cross bands. This can have a negative effect on the
perpendicular properties without adversely affecting the parallel properties.
Recommendations 1. The Australian designers of plywood structures should use the characteristic values
from AS1720.1:2010.
2. The characteristic plywood stresses in AS/NZS2269.0:2008 should either by amended
to reflect those in AS1720.1:2010 or deleted leaving AS1720.1:2010 as the only
source.
3. The planned revision of NZS3603:1993 should be aligned with the AS/NZS4063
series in which normalisation has been discontinued. NZS3603 should also adopt the
appropriate plywood grades and characteristic stresses from AS1720.1:2010
4. Consideration should be given to the introduction of lower shear values in
AS1720.1:2010 on the proviso that there are no significant impacts on the structural
use of plywood.
5. The plywood shear test method in AS/NZS2269.1:2008 should be reviewed to
improve its ability to produce true shear failures.
27
References AS/NZS 2269.0:2008, Plywood—Structural Part 0: Specifications. Standards
Australia/Standards New Zealand.
AS/NZS 2269.1:2008, Plywood—Structural Part 1: Determination of structural properties—
Test methods. Standards Australia/Standards New Zealand.
AS/NZS 2269.2:2007, Plywood—Structural Part 2: Determination of structural properties—
Evaluation methods. Standards Australia/Standards New Zealand
AS/NZS4063.1:2010, Characterization of structural timber Part 1: Test methods. Standards
Australia.
AS1720.1:2010, Timber structures Part 1: Design methods. Standards Australia.
NZS3603:1993 Timber Structures Standard, Standard New Zealand
Acknowledgements Scion wishes to acknowledge
DEEDI for their input on the plywood testing.
Simon Dorries of EWPAA for his input in the sourcing and organisation to get the
plywood to both Scion and DEEDI.
Warwick Banks of CHH Woodproducts for his review of the findings.
The support of the plywood mills in facilitating the collection and supply of the
plywood test sheets both in Australia and New Zealand
Researcher’s Disclaimer The information and opinions provided in the Report have been prepared for the Client and its
specified purposes. Accordingly, any person other than the Client uses the information and
opinions in this report entirely at its own risk. The Report has been provided in good faith and
on the basis that reasonable endeavours have been made to be accurate and not misleading
and to exercise reasonable care, skill and judgment in providing such information and
opinions.
Neither Scion, nor any of its employees, officers, contractors, agents or other persons acting
on its behalf or under its control accepts any responsibility or liability in respect of any
information or opinions provided in this Report.
28
Appendix A Table A1: Summary of AS1720.1:2010 test results for the combined sample
Batches 1, 2, 3 & 4.
Characteristic Strength Properties (MPa)
Strength Property Plywood Test
Direction
NZ
Radiata
F8
(Batch 1)
NZ
Radiata
F11
(Batch 2)
Australian
Radiata
F8 grade
(Batch 3)
Australian
Radiata
F11 grade
(Batch 4)
Bending stiffness Parallel
9665
(10.3%)
[8056]
10720
(10.8%)
[8849]
8970
(11.7%)
[7277]
10432
(11.7%)
[8470]
Bending stiffness Perpendicular
10014
(17.9%)
[7255]
9598
(16.1%)
[7182]
11440
(19.3%)
[8198]
10290
(25.9%)
[7427]
Bending strength Parallel
28.61
(21.9%)
[29.88]
33.05
(23.8%)
[34.63]
29.36
(23.3%)
[30.77]
32.65
(23.3%)
[34.18]
Bending strength Perpendicular
28.60
(26.1%)
[30.45]
25.97
(26.9%)
[27.91]
33.02
27.0%)
[35.60]
34.00
(30.7%)
[38.30]
Tension strength Parallel
17.43
(21.5%)
[17.96]
17.75
(20.5%)
[18.25]
19.23
(24.8%)
[19.92]
21.30
(23.0%)
[21.99]
Tension strength Perpendicular
14.78
(31.0%)
[16.41]
12.26
(32.4%)
[13.85]
20.12
(31.3%)
[22.46]
14.72
(39.9%)
[18.30]
Compression
Strength Parallel
40.05
(5.8%)
[38.89]
29.17
(13.9%)
[31.18]
31.97
(11.2%)
[33.07]
30.66
(13.1%)
[32.44]
Compression
Strength Perpendicular
36.92
(10.2%)
[37.75]
29.14
(17.2%)
[30.13]
35.56
(14.1%)
[38.11]
35.23
(15.2%)
[36.28]
Shear Strength Parallel
5.30
(8.6%)
[5.32]
5.72
(8.2%)
[5.70]
5.48
(15.3%)
[5.65]
5.30
(15.6%)
[5.47]
Shear Strength Perpendicular
5.66
(6.9%)
[5.56]
6.02
(6.8%)
[5.92]
5.74
(11.6%)
[5.97]
5.77
(12.5%)
[6.06]
(10.3%) denotes Coefficient of Variation
[9680] denotes 5th
percentile
29
Table A2: Summary of AS1720.1:2010 test results for the combined sample.
Batches 5, 6, 7 & 8.
Characteristic Strength Properties (MPa)
Strength Property Plywood Test
Direction
Australian
Slash
F11 grade
(Batch 5)
Australian
Slash
F14 grade
(Batch 6)
Australian
Plantation
Hardwood
(Batch 7)
Australian
Hardwood
F34
(Batch 8)
Bending stiffness Parallel
10151
(12.0%)
[8199]
12285
(7.5%)
[10759]
12934
(-)
[-]
22678
(11.7%)
[18407]
Bending stiffness Perpendicular
12109
(21.7%)
[8710]
12311
(19.5%)
[8821]
13736
(-)
[-]
21396
(15.7%)
[16141]
Bending strength Parallel
35.83
(21.6%)
[37.40]
44.54
(17.1%)
[46.07]
38.20
(-)
[-]
99.56
(11.9%)
[103.84]
Bending strength Perpendicular
41.36
(25.3%)
[43.75]
41.20
(24.0%)
[43.21]
40.30
(F-)
[-]
91.11
(17.5%)
[94.31]
Tension strength Parallel
30.34
(17.5%)
[31.08]
28.86
(22.0%)
[29.76]
30.33
(-)
[-]
67.13
(20.7%)
[69.10]
Tension strength Perpendicular
23.43
(30.7%)
[25.93]
23.12
(32.4%)
[26.12]
23.43
(-)
[-]
52.67
(31.5%)
[59.02]
Compression Strength Parallel
27.30
(14.4%)
[29.38]
29.73
(19.7%)
[30.92]
34.64
(-)
[-]
66.85
(9.4%)
[67.65]
Compression Strength Perpendicular
23.31
(25.6%)
[24.71]
40.93
(10.6%)
[42.06]
43.50
(-)
[-]
66.6
(11.6%)
[69.34]
Shear Strength Parallel
5.46
(9.3%)
[5.52]
5.05
(12.6%)
[5.31]
5.91
(-)
[-]
6.52
(11.1%)
[6.74]
Shear Strength Perpendicular
5.07
(13.5%)
[5.39]
5.12
(14.7%)
[5.53]
6.01
(-)
[-]
6.51
(10.5%)
[6.68]
(10.3%) denotes Coefficient of Variation
[9680] denotes 5th
percentile
Note:
The batch 7 material was produced by DEEDI using veneers from four species of plantation
logs, the plywood was laid-up to suit the objectives of another project, and as such is not
directly comparable with production plywood. Hence the Coefficient of Variation and 5th
percentile data has not been included.